RICHARDSON, Texas -- Furmanite Middle has completed work on the third and final phase of a project to replace the upper sections of three risers and emergency shutdown (ESD) valves on a platform offshore Qatar for Occidental Petroleum.
The company replaced top sections of a 6-in., 8-in., and 10-in. (15-cm, 20-cm, and 25-cm) riser and ESD valves on the PS1D platform to enable the risers to be pigged for cleaning purposes. The wall thickness of the existing topside risers was too thick to allow the cleaning pigs to pass through, the company says.
Furmanite used a mechanical bolt-on hot tapping tees, coupled with a custom-developed plugging tool with a special launching arrangement. This involved a set of umbilical hoses run through a steel tube, which was sealed into a housing using a glanded seal arrangement. Furmanite also performed the pipe cutting operations to enable the old riser sections to be removed.
The procedure involved an initial standard hot tap and line stop procedure to create isolation and allow a pipe cut to take place where the temporary mechanical flange was fitted. The purpose-designed plugging tool was bolted on to the mechanical flange. The initial line stop was then retracted and the bespoke plugging tool was launched to achieve isolation at the required point (below the initial line stop). This required deployment along a 2-m (6.6-ft) section of the riser and round the 5D bend.
With the plugging head in place and isolation achieved, the mechanical flange and plug launching tool were removed, and a second pipe cutting operation was carried out at the lower point required to remove the section of riser needing to be replaced. A new section of riser was then welded in place, and the mechanical flange re-fitted to this new section. The line plug could then be moved up the riser, and the process repeated until the point at which the new ESD valve was fitted, when the plug was finally retrieved through the valve.